The invention relates to making composite material parts, and more particularly to making reinforcing fiber textures for such parts.
The field of application of the invention is that of making structural parts out of composite material comprising fiber reinforcement and a resin matrix. Such parts are used in very numerous fields, and in particular in the field of aviation. The reinforcing fiber texture is densified with the resin matrix by any known means, for example by resin transfer molding (RTM).
Another field of application of the invention is making parts out of thermostructural composite material, i.e. out of a material having mechanical properties that enable it to constitute structural elements and having the ability to conserve those properties at high temperatures. Thermostructural composite materials are typically carbon/carbon (C/C) composite materials having carbon reinforcement densified with a carbon matrix, and ceramic matrix composite (CMC) materials having refractory fiber reinforcement (carbon fibers or ceramic fibers) densified with a ceramic matrix. Parts made of thermostructural composite material are used in particular in the fields of aviation and space. The reinforcing fiber texture can be densified with the matrix constituting the material by chemical vapor infiltration (CVI) or by a liquid technique, as is well known. Densification by a liquid technique consists in impregnating the fiber structure with a liquid composition containing a precursor for the material constituting the matrix, typically a resin, and the precursor is transformed by heat treatment.
For composite material parts presenting a certain amount of thickness, it is known to make the reinforcing fiber texture as a plurality of superposed layers that are bonded to one another so as to avoid the layers separating.
Proposals have thus been made, for example in documents U.S. Pat. No. 4,848,414, U.S. Pat. No. 5,899,241 and EP 1 526 285, to make a reinforcing texture by three-dimensional weaving with warp yarns that interlace weft yarns belonging to a plurality of different layers of weft yarns. The weave is of the interlock type with the weft yarns being disposed in a staggered relationship in successive weft planes.
U.S. Pat. No. 5,102,725 also discloses a reinforcing fiber texture with weaving of the satin type that is locally three-dimensional. The fiber texture is constituted by two layers of weft yarns interlaced at certain points by a first warp yarn taking hold in alternation of one yarn in four of the first weft yarn layer and one yarn in eight of the second weft yarn layer. The weft yarns of the second layer of weft yarns are also woven with a second warp yarn using conventional satin type two-dimensional weaving, the two warp yarns extending mainly between the two layers of weft yarns. In the second layer of weft yarns, the same weft yarns are taken by the first and second warp yarns, thereby creating surface irregularities. Furthermore, the technique described of weaving with warp yarns both extending between the two layers of weft yarns is suitable specifically for making a fiber texture of thickness that is limited to two layers of weft yarns.
Various aspects need to be taken into consideration when making such reinforcing fiber textures for composite material parts.
Thus, the three-dimensional weaving must provide satisfactory interlacing between layers so as to oppose delamination, but without that affecting mechanical behavior in directions parallel to the planes of the layers.
In addition, for composite material parts that are to present a smooth surface state, it is desirable to avoid the reinforcing fiber texture presenting large surface irregularities that require additional operations in order to eliminate such irregularities, e.g., after an initial densification stage or consolidation stage, operations such as trimming the surface or adding a two-dimensional ply on the surface, e.g. a cloth ply, prior to finishing off densification.